The focus of this project is an analysis of molecular events involved in homologous recombination in Drosophila. We have taken a biochemical approach to this problem. A protein called Rrp1 (Recombination Repair Protein 1) was purified from Drosophila embryos, which carries out a three-strand in vitro recombination reaction known as strand transfer. The biochemical properties of this protein are similar to the properties of proteins known to be essential in homologous recombination pathways that have been purified from Escherichia coli and Saccharomyces cerevisiae. However, one novel property of Rrp1 is its ability to recognize and cleave abasic sites in DNA, which is not a known property of other proteins that carry out the strand transfer reaction. Recognition of abasic DNA sites is important in order to repair alkylation and oxidative damage to DNA. Therefore, it is possible that the Rrp1 protein is involved in both homologous recombination and DNA repair, or specifically in a recombination repair pathway in Drosophila. The Rrp1 gene has been cloned and sequenced, and a preliminary analysis of the expression pattern has been determined. Overexpression of the Rrp1 protein using an E. coli expression system has recently been achieved. This will allow further physical and enzymatic characterization of the protein to be carried out. In future work a genetic analysis will be necessary to address the biological function of Rrp1 in Drosophila. It seems likely that a role in response to environmental stresses that cause DNA damage will be observed.